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Browsing by Author "Mohseni, O."

Now showing 1 - 3 of 3
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    Dissolved Oxygen Dynamics in Holland Lake, MN
    (St. Anthony Falls Laboratory, 2000-03) Mohseni, O.; Stefan, Heinz G.
    The Minnesota Department of Natural Resources, Division of Fisheries, has been considering Holland Lake for stocking with brown trout. Holland Lake, a Twin Cities Metro Area lake, with a surface area of 0.14 km2 and a maximum depth of about 61 ft (18,8 m) is located in Dakota County, The lake has two shallow subbasins with a substantial amount of rooted vegetation and a deep subbasin, which is thermally suitable for brown trout, However, due to a high oxygen depletion rate in summer, the lake becomes anoxic below the surface mixed layer, A combination of high water temperatures in the surface mixed layer and low dissolved oxygen below the surface mixed layer makes it difficult for brown trout to survive in summer, For possible future aeration of the lake, the dissolved oxygen (DO) dynamics of the lake were studied. Historical records show that DO depletes at a rate of 0.47 mg.l"].day-] after spring oveliu11l in the upper stratum of the metalimnion (from 10 to 20 ft depth), such that the lake develops a negative heterograde DO profile by early July. DO depletes at a lower rate (0.22 mg.1"] .day-I) in the lower stratum of the metalinmion (from 20 to 30 ft depth). By mid-August, the entire metalimnion becomes completely anoxic, To better understand and to quantify the processes that contribute to the DO dynamics in the lake, temperature, DO, Secchi depth, photosynthetically active radiation (P AR), total suspended solids (TSS), total organic carbon (TOC), total respiration rate and chl-a concentrations were monitored or measured at three locations during the SUlIDner of 1999. The Secchi depth varied from 5 to 10 ft (1.5 to 3.0 m)in the deep subbasin and from 2.5 to 9 ft (0.75 to 2.7 m) in the easte11l shallow subbasin. The PAR measurements showed ail attenuation coefficient of about 0.25 ft-I in the deep subbasin; it varied with depth by two orders of magnitude (from 0.2 ft-) to 25 fr]) in the shallow subbasins, indicating increasing macrophyte density with depth. In the deep subbasin, the TSS concentration varied from 1 to 3 mgll with a maximum of 5 mgll in the upper stratum of the metalimnion. About 76% of the TSS were volatile, which indicates that most if not all TSS is organic material. Carbonaceous biological oxygen demand (CBOD) was estimated using the TOC profiles. The average CBOD was 18.7 mg/l, with a maximum of 24 mgll in the upper stratum of the metalimnion.
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    Groundwater Interactions with Holland Lake, MN
    (St. Anthony Falls Laboratory, 2001-07) Mohseni, O.; Stefan, H. G.
    Holland Lake, a small but deep mesotrophic lake in the Twin Cities Metropolitan Area, has been considered by the Minnesota Department of Natural Resources, Division of Fisheries, for stocking with brown trout. Holland Lake, with a surface area of 0.14 km:2 (35 acres) and a maximum depth of about 18.8 m (61 ft) consists of two shallow bays covered with rooted macrophytes and a deep main basin. The deep basin is thermally suitable for brown trout. However, due to a high oxygen depletion rate in summer, the lake becomes anoxic below the surface mixed layer. The field study conducted in the summer of 1999 by the authors concluded that several mechanisms, all regarding some sort of horizontal advection process, could explain the observed high dissolved oxygen (DO) depletion rates: transport of detrital material from the shallow bays, density currents combined with sediment oxygen demand in the shallow bays and flushing effect by groundwater flow through the lake. Density currents from the shallow bays were attributed to the temperature regimes of the shallow bays. To aid in the design of an aeration system for the lake, a new field study was conducted in the summer of 2000 to quantify the potential groundwater flow through the lake, especially through the shallow bays. The field study included the measurement of groundwater piezometric heads underneath the lake bed using a potentiomanometer and DO concentrations and temperatures of groundwater. In addition, the water temperature profiles were measured at several locations in the shallow bays to investigate the potential for density currents.
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    Uncertainties in Projecting Stream flows in Two Watersheds Under 2xC02 Climate Conditions
    (St. Anthony Falls Laboratory, 1998-03) Mohseni, O.; Hanratty, M. P.; Stefan, H. G.
    Two surface water runoff models (SWAT and MINRUN96) were utilized to project changes in streamflows in two watersheds under a 2xC02 climate scenario, One is the Baptism River watershed (363 km2), in northern Minnesota, mainly forested, with a cold and humid climate, and the other is the Little Washita River watershed, in Oklahoma (538 km\ an agricultural watershed, with a warm and seasonally dry climate, 2xC02 climate conditions were obtained from the Canadian Climate Center General Circulation Model. No agreement was evident in the streamflows projected by the two watershed models for the Baptism River. Snow accumulation and snowmelt were the main differences between the two models. MINRUN96 simulated the past streamflow more accurately than SWAT. SWAT includes a biomass submodel which incorporates the effects of vegetation changes under 2xC02 climate conditions. SWAT also takes into account the effects of carbon dioxide in the estimation of evapotranspiration, while MINRUN96 does not contain any algorithm projecting the changes in vegetation or evapotranspiration due to doubling of atmospheric carbon dioxide. Both models projected more runoff in the Baptism River watershed in winter due to reduced snowfall under the 2xC02 climate scenario; however, the magnitudes of the projected increases were an order of magnitude different. SWAT was developed for agricultural watersheds and is probably not ,suited for application to forested watersheds at this time. For the Little Washita River watershed, the streamflows projected by the two models were in agreement. Both models showed an increase in fall and spring runoff and a decrease in summer runoff. The two models also proj ected a significant increase in the mmual streamflow of the Little Washita River under a 2xC02 climate scenario. The magnitUdes of the projected increases were comparable.